Herpes simplex viruses (HSVs) cause a variety of human diseases, including cold sores, eye and genital infections, neonatal infections and encephalitis. Both serotypes, HSV1 and HSV2, establish lifelong latent infections within sensory ganglia. Because HSV has a complex interaction with its host, it is not surprising that the envelope contains eleven virus-encoded glycoproteins. These proteins function in virus entry, spread, immune evasion and inhibition of apoptosis. In addition, the virus can enter cells via several different receptors. Many strains of HSV1 and 2 can use two of these, HveA (herpes virus entry mediator A) and nectin-1 (HveC). HveA is found in copious amounts on T lymphocytes and to a lesser extent on other cell types. Nectin-1 is a cell adhesion molecule that is abundant on epithelial and neuronal cells. Our goal is to increase our understanding of the interaction between nectin-1 and gD, the receptor binding protein of HSV and to determine the significance of this interaction for HSV infection in cells and in vivo. Solution of the structure of gD alone or bound to HveA revealed that two conformational changes in gD occur when it binds HveA. We hypothesize that at least one of these also occurs when gD binds nectin-1 and may be important for the role of gD in later steps of entry. Therefore, solving the structure of the gD/nectin-1 complex is a major goal of this project. Nectin-1 can interact in trans with itself as well as with other nectins at cellular adherens junctions. We speculate that newly synthesized gD acts as a ligand for nectin-1 on adjacent uninfected cells, thereby ensuring that receptor is available for the virus to spread to the next cell. We further hypothesize that nectin-1 is down regulated from the infected cell surface and therefore does not impede virus spread to the next cell. Finally, we have constructed a panel of gD mutants with defined receptor usage. We will recombine these into the viral genome and test their ability to cause primary and zosteriform disease in a mouse model. The aims of this grant are: (1) to characterize the interaction between gD and nectin-1; (2) to explore the effects of gD and HSV infection on nectin-1 mediated functions; and (3) to determine the role of nectin-1 and other HSV entry receptors in a mouse model of virus infection.